The subcarrier allocation problem in cognitive radio（CR）networks with multi-user orthogonal frequency-division multiplexing（OFDM）and distributed antenna is analyzed and modeled for the flat fading channel and the ...The subcarrier allocation problem in cognitive radio（CR）networks with multi-user orthogonal frequency-division multiplexing（OFDM）and distributed antenna is analyzed and modeled for the flat fading channel and the frequency selective channel,where the constraint on the secondary user（SU）to protect the primary user（PU）is that the total throughput of each PU must be above the given threshold instead of the ＂interference temperature＂.According to the features of different types of channels,the optimal subcarrier allocation schemes are proposed to pursue efficiency（or maximal throughput）,using the branch and bound algorithm and the 0-1 implicit enumeration algorithm.Furthermore,considering the tradeoff between efficiency and fairness,the optimal subcarrier allocation schemes with fairness are proposed in different fading channels,using the pegging algorithm.Extensive simulation results illustrate the significant performance improvement of the proposed subcarrier allocation schemes compared with the existing ones in different scenarios.展开更多
A power allocation scheme for multi-user multiple-input multiple-output orthogonal frequency division multiplexing （MI- MO-OFDM） systems with channel state information （CSI） on transmitter and receiver is pressed....A power allocation scheme for multi-user multiple-input multiple-output orthogonal frequency division multiplexing （MI- MO-OFDM） systems with channel state information （CSI） on transmitter and receiver is pressed. Multi-user lower allocation can be decoupled into single user lower allocation throughout null space mapping of multi-user channel and lower allocation can be performed throughout spatial-spectral water-filling for per user.To deal with more users in system and fading correlation,scheduling is oerformed to maintain the gain of power allocation.The proposed scheme can substantially improve system＇s spectral efficiency with low complexity.Simulation results validate the accuracy of theoretic analyses.展开更多
An iterative receiver is proposed based on the EM (Expectation-Maximization)algorithm for an OFDM-SDMA (Orthogonal Frequency Division Multiplexing-Space Division Multiple Access) system. By using a few pilots in every...An iterative receiver is proposed based on the EM (Expectation-Maximization)algorithm for an OFDM-SDMA (Orthogonal Frequency Division Multiplexing-Space Division Multiple Access) system. By using a few pilots in every OFDM symbol, both channel estimation and multiuser detection can be simultaneously obtained by iteration. The computer simulation results show this receiver can track channel variations and detect multiuser symbols for different number of users under time-varying multipath channels.展开更多
In this work, two popular evolutionary algorithms such as genetic algorithm (GA) and particle swarm optimization (PSO) based SDMA-OFDM multi user detection (MUD) have been presented which overcome the limitations of c...In this work, two popular evolutionary algorithms such as genetic algorithm (GA) and particle swarm optimization (PSO) based SDMA-OFDM multi user detection (MUD) have been presented which overcome the limitations of classical detectors. They are simple to implement and their complexity in terms of decision-metric evaluations is very less compared to maximum likelihood detection (MLD). These techniques are shown to provide a high performance as compared to the other detectors especially in a rank-deficient scenario where numbers of users are high as compared to the base station (BS) antennas. In this scenario, Zero forcing (ZF) and minimum mean square error (MMSE) based MUDs exhibit severe performance degradation. To investigate almost realistic performance of a wireless communication system, it is important to use a proper channel model. Since the simulation parameters in this work are based on IEEE 802.11n wireless local area network (WLAN) standard, TGn is the channel model used.展开更多
This paper deals with design and analysis of user scheduling and power allocation for multi-antenna OFDM systems with DPC,ZF-DPC,ZF-BF and TDMA transmit strategies.We consider the general multi-user downlink schedulin...This paper deals with design and analysis of user scheduling and power allocation for multi-antenna OFDM systems with DPC,ZF-DPC,ZF-BF and TDMA transmit strategies.We consider the general multi-user downlink scheduling problem and power minimization with multi-user rate constraints.According to the channel state,it is shown that there is a power optimal policy which selects a subset of users in each scheduling interval.We present user selection algorithms for DPC,ZF-DPC,ZF-BF and TDMA for multi-antenna OFDM system in broadcast channels,and we also present the practical water-filling solution in this paper.By the selected users with the consideration of fairness,we derive the power optimization algorithm with multi-user rate constraints.We also analyze the power duality of uplink-downlink for the transmit strategies of DPC,ZF-DPC and ZF-BF.Simulation results show that the present user-scheduling algorithm and power minimization algorithm can achieve good power performance,and that the scheduling algorithm can guarantee fairness.展开更多
The problem of the simultaneous multi-user resource allocation algorithm in orthogonal frequency division multiple access(OFDMA)based systems has recently attracted significant interest.However,most studies focus on m...The problem of the simultaneous multi-user resource allocation algorithm in orthogonal frequency division multiple access(OFDMA)based systems has recently attracted significant interest.However,most studies focus on maximizing the system throughput and spectral efficiency.As the green radio is essential in 5G and future networks,the energy efficiency becomes the major concern.In this paper,we develop four resource allocation schemes in the downlink OFDMA network and the main focus is on analyzing the energy efficiency of these schemes.Specifically,we employ the advanced multi-antenna technology in a multiple input-multiple output(MIMO)system.The first scheme is based on transmit spatial diversity(TSD),in which the vector channel with the highest gain between the base station(BTS)and specific antenna at the remote terminal(RT)is chosen for transmission.The second scheme further employs spatial multiplexing on the MIMO system to enhance the throughput.The space-division multiple-access(SDMA)scheme assigns single subcarrier simultaneously to RTs with pairwise“nearly orthogonal”spatial signatures.In the fourth scheme,we propose to design the transmit beamformers based on the zero-forcing(ZF)criterion such that the multi-user interference(MUI)is completely removed.We analyze the tradeoff between the throughput and power consumption and compare the performance of these schemes in terms of the energy efficiency.展开更多
In this paper, distributed relay diversity systems are analyzed, modeled and evaluated in an Orthogonal Frequency Division Multiplexing (OFDM) based networks. The investigated distributed relay diversity schemes exten...In this paper, distributed relay diversity systems are analyzed, modeled and evaluated in an Orthogonal Frequency Division Multiplexing (OFDM) based networks. The investigated distributed relay diversity schemes extend the ideas of a single hop transmit antenna schemes such as Cyclic Delay Diversity (CDD), Space Time Transmit Diversity (STTD), transmit Coherent Combining (CC) and Selection Diversity (SD) to distributed diversity systems. In contrast to the classical single hop system, the antennas in the distributed systems belongs to distributed relays instead of being co-located at the transmitter. The distributed relay diversity methods considered in this paper: Relay CDD (RCDD), Relay Alamouti (i.e.STTD), Relay CC (RCC) and Relay SD (RSD) are compared to the traditional 1-hop system. Analytical expressions for the received Signal to Interference Noise Ratio (SINR) are derived and used in a dynamic multi-cell multi-user simulator. Results show considerable SINR gains for both Round Robin and Max-SINR schedulers. The SINR gains translate into substantial cell throughput gains, up to 200%, compared to 1-hop systems. Despite its low complexity, the RCDD scheme has similar performance to that of other more sophisticated 2-hop schemes such as Relay Alamouti and Relay Coherent Combining. Marginally better results are observed for the Relay Selection Diversity scheme.展开更多
In OFDM-based System such as long term evolution （LTE）, the scheduling scheme plays an essential role in not only improving the capacity of system, but also guarantee the fairness among the user equipments （UEs）. ...In OFDM-based System such as long term evolution （LTE）, the scheduling scheme plays an essential role in not only improving the capacity of system, but also guarantee the fairness among the user equipments （UEs）. However, most existing work about scheduling only considers the current throughput in physical layer. Thus in this paper, a cross-layer scheduling with fairness based on restless bandit （CSFRB） scheme with the ＇indexability＇ property is proposed for the multi-user orthogonal frequency-division multiplexing （OFDM） system to minimize the distortion in the application layer, to maximize the throughput and to minimize the energy consumption in the physical layer. The scheduling problem is firstly established as a restless bandit problem, which is solved by the primal-dual index heuristic algorithm based on the first order relaxation with low complexity, to yield the CSFRB scheme. AdditionaUy, this scheme is divided into offiine computation and online selection, where main work will be finished in former one so as to decrease the complexity further. Finally, extensive simulation results illustrate the significant performance improvement of the proposed CSFRB scheme compared to the existing one in different scenarios.展开更多
The work proposes two novel spreading codes, called extensive double-orthogonal code （EDOC） and flexible paired-orthogonal code （FPOC）, for multi-user downlink multiple-input multiple-output （M1MO） orthogonal fr...The work proposes two novel spreading codes, called extensive double-orthogonal code （EDOC） and flexible paired-orthogonal code （FPOC）, for multi-user downlink multiple-input multiple-output （M1MO） orthogonal frequency division multiplexing （OFDM） systems. The goal of code designs is to obtain an improved bit error rate （BER） performance without loss of bandwidth efficiency. The code designs achieve space diversity by employing multiple antennas at both transmit ends and receive ends. Codes are reasonably spread into time, frequency and space domain. The proposed codes are attractively characterized with length flexibility, which breaks the ＂power of two＂ constraint. The simulation results indicate that the proposed codes improve overall BER performance, by exploiting space diversity gains. The flexibility in code length also results in high spectral efficiency.展开更多
The paper thinks that China should begin studying B3G as early as possible,participate in the establishment of international standards and draft its own set of standards especially.It briefs the four development trend...The paper thinks that China should begin studying B3G as early as possible,participate in the establishment of international standards and draft its own set of standards especially.It briefs the four development trends of contemporary infocommunications based on four related laws and the development of mobile communications.It discusses the development goal of B3G in China and points out that among the B3G related technologies,the effective spectrum and coverage technologies as well as pure IP architecture should be studied in strength.展开更多
Multi-access interference(MAI)is the main source limiting the capacity and quality of the multiple-input multipleoutput orthogonal frequency division multiplexing(MIMO-OFDM)system which fulfills the demand of high-spe...Multi-access interference(MAI)is the main source limiting the capacity and quality of the multiple-input multipleoutput orthogonal frequency division multiplexing(MIMO-OFDM)system which fulfills the demand of high-speed transmission rate and high quality of service for future underwater acoustic(UWA)communication.Therefore,multi-user detection(MUD)is needed at the receiver of the MIMO-OFDM system to suppress the effect of MAI.In this research,MUD is achieved by using a criterion based adaptive recursive successive interference cancellation(RSIC)scheme at the receiver of a MIMO-OFDM system whose transceiver model in underwater communication is implemented by using the Bellhop simulation system.The proposed scheme estimates and eliminates the MAI through user signal detection and subtraction from received signals at the receiver of the MIMO-OFDM system in underwater environment.The bit error rate(BER)performance of the proposed scheme is analyzed by using weight filtering and weight selection criteria.By Matlab simulation,it is shown that the BER performance of the proposed scheme outperforms the conventional matched filter(MF)detector,the adaptive successive interference cancellation(SIC)scheme,and the adaptive RSIC scheme in the UWA network.展开更多
基金The National Natural Science Foundation of China(No.60832009)Beijing Municipal Natural Science Foundation(No.4102044)National Major Science & Technology Project(No.2009ZX03003-003-01)
文摘The subcarrier allocation problem in cognitive radio（CR）networks with multi-user orthogonal frequency-division multiplexing（OFDM）and distributed antenna is analyzed and modeled for the flat fading channel and the frequency selective channel,where the constraint on the secondary user（SU）to protect the primary user（PU）is that the total throughput of each PU must be above the given threshold instead of the ＂interference temperature＂.According to the features of different types of channels,the optimal subcarrier allocation schemes are proposed to pursue efficiency（or maximal throughput）,using the branch and bound algorithm and the 0-1 implicit enumeration algorithm.Furthermore,considering the tradeoff between efficiency and fairness,the optimal subcarrier allocation schemes with fairness are proposed in different fading channels,using the pegging algorithm.Extensive simulation results illustrate the significant performance improvement of the proposed subcarrier allocation schemes compared with the existing ones in different scenarios.
基金This project was supported bythe National Natural Science Foundation of China (60272079) the National High Technol-ogy Research and Development Plan Project of China (2001AA123014) .
文摘A power allocation scheme for multi-user multiple-input multiple-output orthogonal frequency division multiplexing （MI- MO-OFDM） systems with channel state information （CSI） on transmitter and receiver is pressed. Multi-user lower allocation can be decoupled into single user lower allocation throughout null space mapping of multi-user channel and lower allocation can be performed throughout spatial-spectral water-filling for per user.To deal with more users in system and fading correlation,scheduling is oerformed to maintain the gain of power allocation.The proposed scheme can substantially improve system＇s spectral efficiency with low complexity.Simulation results validate the accuracy of theoretic analyses.
基金Supported by the National Natural Science Foundation of China (No. 60272079)
文摘An iterative receiver is proposed based on the EM (Expectation-Maximization)algorithm for an OFDM-SDMA (Orthogonal Frequency Division Multiplexing-Space Division Multiple Access) system. By using a few pilots in every OFDM symbol, both channel estimation and multiuser detection can be simultaneously obtained by iteration. The computer simulation results show this receiver can track channel variations and detect multiuser symbols for different number of users under time-varying multipath channels.
文摘In this work, two popular evolutionary algorithms such as genetic algorithm (GA) and particle swarm optimization (PSO) based SDMA-OFDM multi user detection (MUD) have been presented which overcome the limitations of classical detectors. They are simple to implement and their complexity in terms of decision-metric evaluations is very less compared to maximum likelihood detection (MLD). These techniques are shown to provide a high performance as compared to the other detectors especially in a rank-deficient scenario where numbers of users are high as compared to the base station (BS) antennas. In this scenario, Zero forcing (ZF) and minimum mean square error (MMSE) based MUDs exhibit severe performance degradation. To investigate almost realistic performance of a wireless communication system, it is important to use a proper channel model. Since the simulation parameters in this work are based on IEEE 802.11n wireless local area network (WLAN) standard, TGn is the channel model used.
基金Project supported by the National Natural Science Foundation of China (No. 60572157)the Key Laboratory of Universal Wireless Communication of the Ministry of Education,China (No. 2007103)
文摘This paper deals with design and analysis of user scheduling and power allocation for multi-antenna OFDM systems with DPC,ZF-DPC,ZF-BF and TDMA transmit strategies.We consider the general multi-user downlink scheduling problem and power minimization with multi-user rate constraints.According to the channel state,it is shown that there is a power optimal policy which selects a subset of users in each scheduling interval.We present user selection algorithms for DPC,ZF-DPC,ZF-BF and TDMA for multi-antenna OFDM system in broadcast channels,and we also present the practical water-filling solution in this paper.By the selected users with the consideration of fairness,we derive the power optimization algorithm with multi-user rate constraints.We also analyze the power duality of uplink-downlink for the transmit strategies of DPC,ZF-DPC and ZF-BF.Simulation results show that the present user-scheduling algorithm and power minimization algorithm can achieve good power performance,and that the scheduling algorithm can guarantee fairness.
文摘The problem of the simultaneous multi-user resource allocation algorithm in orthogonal frequency division multiple access(OFDMA)based systems has recently attracted significant interest.However,most studies focus on maximizing the system throughput and spectral efficiency.As the green radio is essential in 5G and future networks,the energy efficiency becomes the major concern.In this paper,we develop four resource allocation schemes in the downlink OFDMA network and the main focus is on analyzing the energy efficiency of these schemes.Specifically,we employ the advanced multi-antenna technology in a multiple input-multiple output(MIMO)system.The first scheme is based on transmit spatial diversity(TSD),in which the vector channel with the highest gain between the base station(BTS)and specific antenna at the remote terminal(RT)is chosen for transmission.The second scheme further employs spatial multiplexing on the MIMO system to enhance the throughput.The space-division multiple-access(SDMA)scheme assigns single subcarrier simultaneously to RTs with pairwise“nearly orthogonal”spatial signatures.In the fourth scheme,we propose to design the transmit beamformers based on the zero-forcing(ZF)criterion such that the multi-user interference(MUI)is completely removed.We analyze the tradeoff between the throughput and power consumption and compare the performance of these schemes in terms of the energy efficiency.
文摘In this paper, distributed relay diversity systems are analyzed, modeled and evaluated in an Orthogonal Frequency Division Multiplexing (OFDM) based networks. The investigated distributed relay diversity schemes extend the ideas of a single hop transmit antenna schemes such as Cyclic Delay Diversity (CDD), Space Time Transmit Diversity (STTD), transmit Coherent Combining (CC) and Selection Diversity (SD) to distributed diversity systems. In contrast to the classical single hop system, the antennas in the distributed systems belongs to distributed relays instead of being co-located at the transmitter. The distributed relay diversity methods considered in this paper: Relay CDD (RCDD), Relay Alamouti (i.e.STTD), Relay CC (RCC) and Relay SD (RSD) are compared to the traditional 1-hop system. Analytical expressions for the received Signal to Interference Noise Ratio (SINR) are derived and used in a dynamic multi-cell multi-user simulator. Results show considerable SINR gains for both Round Robin and Max-SINR schedulers. The SINR gains translate into substantial cell throughput gains, up to 200%, compared to 1-hop systems. Despite its low complexity, the RCDD scheme has similar performance to that of other more sophisticated 2-hop schemes such as Relay Alamouti and Relay Coherent Combining. Marginally better results are observed for the Relay Selection Diversity scheme.
基金supported by the National Natural science Foundation of China (2009ZX03002-014)the National Youth Science Foundation (61001115)
文摘In OFDM-based System such as long term evolution （LTE）, the scheduling scheme plays an essential role in not only improving the capacity of system, but also guarantee the fairness among the user equipments （UEs）. However, most existing work about scheduling only considers the current throughput in physical layer. Thus in this paper, a cross-layer scheduling with fairness based on restless bandit （CSFRB） scheme with the ＇indexability＇ property is proposed for the multi-user orthogonal frequency-division multiplexing （OFDM） system to minimize the distortion in the application layer, to maximize the throughput and to minimize the energy consumption in the physical layer. The scheduling problem is firstly established as a restless bandit problem, which is solved by the primal-dual index heuristic algorithm based on the first order relaxation with low complexity, to yield the CSFRB scheme. AdditionaUy, this scheme is divided into offiine computation and online selection, where main work will be finished in former one so as to decrease the complexity further. Finally, extensive simulation results illustrate the significant performance improvement of the proposed CSFRB scheme compared to the existing one in different scenarios.
基金supported by the Shandong Province Natural Science Foundation (ZR2010FQ008)
文摘The work proposes two novel spreading codes, called extensive double-orthogonal code （EDOC） and flexible paired-orthogonal code （FPOC）, for multi-user downlink multiple-input multiple-output （M1MO） orthogonal frequency division multiplexing （OFDM） systems. The goal of code designs is to obtain an improved bit error rate （BER） performance without loss of bandwidth efficiency. The code designs achieve space diversity by employing multiple antennas at both transmit ends and receive ends. Codes are reasonably spread into time, frequency and space domain. The proposed codes are attractively characterized with length flexibility, which breaks the ＂power of two＂ constraint. The simulation results indicate that the proposed codes improve overall BER performance, by exploiting space diversity gains. The flexibility in code length also results in high spectral efficiency.
文摘The paper thinks that China should begin studying B3G as early as possible,participate in the establishment of international standards and draft its own set of standards especially.It briefs the four development trends of contemporary infocommunications based on four related laws and the development of mobile communications.It discusses the development goal of B3G in China and points out that among the B3G related technologies,the effective spectrum and coverage technologies as well as pure IP architecture should be studied in strength.
文摘Multi-access interference(MAI)is the main source limiting the capacity and quality of the multiple-input multipleoutput orthogonal frequency division multiplexing(MIMO-OFDM)system which fulfills the demand of high-speed transmission rate and high quality of service for future underwater acoustic(UWA)communication.Therefore,multi-user detection(MUD)is needed at the receiver of the MIMO-OFDM system to suppress the effect of MAI.In this research,MUD is achieved by using a criterion based adaptive recursive successive interference cancellation(RSIC)scheme at the receiver of a MIMO-OFDM system whose transceiver model in underwater communication is implemented by using the Bellhop simulation system.The proposed scheme estimates and eliminates the MAI through user signal detection and subtraction from received signals at the receiver of the MIMO-OFDM system in underwater environment.The bit error rate(BER)performance of the proposed scheme is analyzed by using weight filtering and weight selection criteria.By Matlab simulation,it is shown that the BER performance of the proposed scheme outperforms the conventional matched filter(MF)detector,the adaptive successive interference cancellation(SIC)scheme,and the adaptive RSIC scheme in the UWA network.
